This method relates generally to medical catheters, and in particular to a new torque control and rotation limiting mechanism for manipulating the tip of such a catheter by rotating it within a patient's body. Typically, a medical catheter is introduced into a patient and is advanced through paths of variable tortuosity to a treatment site. The path may be fairly straight, or may have many turns in it. The catheter conventionally includes a means for treatment of the patient at a treatment site, such as by balloon dilatation, delivery of mechanical, electromagnetic or laser energy for ablation or removal of atherosclerotic material, angioscopic delivery, delivery of contrast media to tissue at the treatment site, and so on.
In many cases, it is necessary to rotate the catheter tip, either to steer the catheter in a desired direction as it is being introduced into the patient toward the treatment site, or to reposition the catheter tip by rotating it about an axis, thus repositioning the treatment means. Rotation of the catheter tip can be quite difficult. Typically, a medical catheter is designed to be as flexible as possible, in order to allow it to negotiate the curves encountered in the body when positioning the tip at the treatment site, and to make it as atraumatic to the patient as possible. However, the more flexible the catheter, the lower the torsional stiffness will generally be, and thus a compromise must be made between flexibility and stiffness. When the torsional stiffness is low, a single rotation of the proximal end of the catheter may result in less than one full rotation of the distal end of the catheter; for instance, a 360.degree. rotation at the proximal end may result in 180.degree. or less of rotation at the distal end.
Therefore, there is a need for a device which will rotate the tip of a catheter in a reliable manner, and which will minimize the ratio of turns necessary at the proximal end to accomplish a single turn at the distal end.
It is undesirable to twist a catheter too much, since the treatment means, guide wire, fiber optics or other devices within the catheter will become twisted around one another. Thus, there is also a need for a means for limiting the rotational travel of a catheter tip when it is within the patient.
In particular, there is a need for a device wherein no compromise is necessary between the flexibility of the catheter body and the rotational control of the catheter tip.